The present invention relates to a method for evaluating a color tone of a coating film and a device for this evaluation.
As a coating film, there is a metallic film 1 made by that a paint containing a color pigment 11 and a gloss material 12 is applied as seen in FIG. 1, on which a clear paint is applied. Hereupon, the gloss material refers to a pigment in which alumina or a mica flake is a material and the surface emits gloss. A metallic film of this kind has practically been used, for example, as a coating film for an automobile body, so that it has a great effect on whether the outlook of an automobile is superior or inferior. Therefore, to make a reasonable relationship with this outlook, evaluation of a color tone of a coating film is very important.
Hitherto, the evaluation of a color tone of a coating film has been carried out according to the undermentioned methods.
That is, there are methods wherein, in a reflecting light upon projecting a luminous flux for a coating film, a high light part which is in an angle range adjacent to the regularly reflecting luminous flux, and a shade part which is in an angle range apart from said regularly reflecting luminous flux are separately and simply subjected to photoelectric detection, their luminous intensities are measured and the intensities obtained are treated with operation, and difference between the lightness of the coating film surface in a case of that the surface is seen from a direction adjacent to the regularly reflecting luminous flux and the lightness of the coating film surface in a case of that the surface is seen from a direction apart from the regularly reflecting luminous flux is investigated to evaluate the color tone of a coating film (Japanese Official Patent Provisional Publication, showa 59-180441; Japanese Official Patent Gazette, showa 57-11014; Japanese Official Patent Gazette, showa 60-59866; and Japanese Official Patent Provisional Publication, showa 62-160166).
In these previous methods, although an attempt to enhance accuracy for the evaluation is made by using a respectively proper equation in the operation treatment, all the methods are after all such that the color tone of a coating film is evaluated by simply looking at a difference between the luminous intensity at a high light part and the one at a shade part. The difference between the luminous intensity at a high light part and the one at a shade part appears as a contrast (flip-flop) feeling on a coating film surface. That is, the previous methods are that, if those are referred to a case of that an observer looks at an automobile body, a color tone is evaluated by that an extent of a contrast feeling on the body surface is expressed with an objective numeral value on a basis of the difference in the luminous intensities.